This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087423 #18 Mar 26 2024 14:45:17
%S A087423 32,768,20672,565248,15491072,424685568,11643256832,319215894528,
%T A087423 8751751626752,239941585993728,6578336360824832,180354352643309568,
%U A087423 4944668491903926272,135565048129674805248,3716706651755063017472,101898745479045492768768
%N A087423 a(n) = S(3*n,3)/S(n,3) where S(n,m) = Sum_{k=0..n} binomial(n,k)*Fibonacci(m*k).
%H A087423 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (32,-128,64).
%F A087423 a(n) = 4^n + (14+6*sqrt(5))^n + (14-6*sqrt(5))^n.
%F A087423 G.f.: -32*x*(6*x^2-8*x+1) / ((4*x-1)*(16*x^2-28*x+1)). - _Colin Barker_, Dec 01 2012
%t A087423 LinearRecurrence[{32,-128,64},{32,768,20672},20] (* _Harvey P. Dale_, Feb 17 2018 *)
%Y A087423 Cf. A020876.
%K A087423 nonn,easy
%O A087423 1,1
%A A087423 _Benoit Cloitre_, Oct 22 2003